Method for the contactless measurement of an object

ABSTRACT

The invention relates to a method for the contactless measurement of an object in at least one dimension. An object is scanned in a spatially restricted effective zone of a scanning beam field and the size of the object in terms of the measured dimension is deduced by the detection of one or more interruptions in the scanning beams. The scanning beam field is constructed from a number of directly addressable individual beams. The beam-assisted scanning of the spatially restricted effective zone of the scanning beam field is carried out according to a predefinable pattern of steps, using a non-linear soiling method.

The invention relates to a process for contactless measurement of anobject as claimed in the preamble of claim 1.

In industrial processes it is often necessary to determine the extensionof an object in height and/or width and/or length in a firstapproximation, so that it can be considered accordingly in a followingtransport, storage and/or processing step. For example, in an automaticwarehouse system the height of the object to be stored must bedetermined. Many objects cannot be measured using sensors with contactsor the like, but contactless methods must be used. Therefore, forexample, light gratings or light curtains which are passed by the objectare used for these automated measurement processes. Measurement takesplace by ascertaining the beam interruptions from which the measurementin the respective dimension can be deduced. In height measurement, theobject projects generally from underneath into the light grating sinceit is being transported on a pallet or a conveyor belt through the lightgrating or the light curtain. Height measurement is finding theuppermost interrupted or lowermost uninterrupted light beam. To do this,in a light grating or light curtain the individual light beams arescanned in sequence in order to ascertain the interruptions. Thescanning of a light beam consists in activating a transmitting elementand at the same time evaluating an opposite receiving element for thetransmitted light beam. The theoretical duration of a scan, the scanningtime, is formed from the scanning time per light beam multiplied by thenumber n of light beams, plus the evaluation time. The equation for itreads:t _(Scan) =t _(Beam) ×n+t _(Evaluation)

It can happen that the object which is to be automatically measured thentravels exactly into the detection area of a light beam after it hasbeen scanned.

In order to preclude this error source and still detect the object, theentire light grating must be scanned a second time. Thus, in practicethe maximum detection time is twice the scanning time. The equation forthe detection time is:t _(detection) =t _(Scan)×2=(t _(Beam) ×n+t _(Evaluation))×2

In practice the scanning time per light beam is roughly 100microseconds; the number n of beams of the light grating is for example32; the evaluation time is typically roughly 500 microseconds. Withthese typical practical values for the maximum detection timet_(detection) the value is 7.4 ms. Here it should be noted that thisvalue is the maximum detection time for determining the extension inonly one dimension, the height. Often it can be necessary to determinethe dimensions of an object in two dimensions or even in all threedimensions. It is immediately apparent from this that the currentprocess for contactless measurement of an object is relativelytime-consuming.

The object of this invention is therefore to avoid this disadvantage ofthe process of the prior art. A process for contactless measurement ofan object in at least one dimension will be devised which enables anincrease in measurement speed with the accuracy remaining the same andwhich leads overall to a shortening of the maximum detection time.

This object is achieved in a process for contactless measurement of anobject which has the features cited in the characterizing section ofclaim 1. Developments and/or advantageous versions of the invention arethe subject of the dependent claims.

The invention proposes a process for contactless measurement of anobject (6) in at least one dimension in which the object (6) is scannedin a three-dimensional limited action area of a scanning beam field (1)and from the detection of one or more interruptions of the scanningbeams (L) the size of the object (6) in the measured dimension isdeduced. The scanning beam field (1) is built up from a number ofdirectly addressable individual beams (L). The beam scanning of thethree-dimensionally limited action area of the scanning beam field (1)takes place according to a definable step pattern using a sortingprocess which is different from a linear sorting process. One preferredprocess consists in using a binary search process.

The detection time for measurement of an object is largely determined bythe duration and the number of scanning steps. A reduction of thescanning steps in the determination of object size therefore actsdirectly on the time interval required for this purpose. The scanningprocess for determination of the beam interruptions is reduced to anonlinear sorting process since the action area of the scanningradiation can be regarded as a scanning beam field which is made up ofindividual, directly addressable beams. Accordingly the principle of anonlinear sorting process can be applied to this field.

In one especially advantageous process, for determining the size of theobject in at least one dimension, the three-dimensionally limited actionarea of the scanning beam field is scanned in regions according to thebinary search principle. The binary search process is based on acontinuous halving of the search interval with simultaneous use ofsorting. For this purpose the action area of the radiation field isbroken down into a number of directly addressable individual beams whichis assigned a continuously increasing or decreasing number for purposesof sorting. The individual beams can be actual measurement beams. Theycan however also be regarded as imaginary measurement beams when theobject is detected for example by an imaging system and the generatedimage is electronically scanned “in beam form” for “beam interruptions”.The binary search system is superior to the linear search system withrespect to the time requirement. For a larger number of individual beansthe time difference increases very quickly. While the operating timeincreases in proportion to the number of scanning beams in a linearsearch, it increases in a binary search only in relation to thelogarithm of the number of scanning beams to the base 2.

Rather it is necessary to determine the size of the object in more thanone dimension. To do this, the three-dimensionally limited action areaof the scanning beam field is advantageously scanned by a combination ofthe principles of linear and binary search. Combining the linear andbinary search takes into account the circumstance that the object whichis to be measured is conventionally taansported into the scanning beamfield in an arbitrary orientation. Therefore it is necessary first ofall to determine in the respective dimension which is to be measured thestart, i.e. the outermost edge of the object, from which the measurementof the object in the respective dimension are determined. This firststep corresponds essentially to one origin determination at a time andis carried out sequentially in a linear search process. After the originhas been ascertained, the actual further measurement of the object canbe simplified and shortened by using the binary search process.

To carry out the process as claimed in the invention the object to bemeasured is placed in a curtain fixed by the scanning beams. In doing sofor example there is a fixed number of radiation sources at regularintervals on top of one another on one lengthwise side of the transportbelt. On the other lengthwise side of the transport belt, opposite theradiation sources, the same number of detectors for the radiationemitted by the radiation sources are arranged on top of one another. Theobject which is to be measured in one dimension is moved via thetransport belt into the area of the scanning beams and is measured thereaccording to the process as claimed in the invention. For measuring theobject in two or in all three dimensions also a flat orthree-dimensional grating can be fixed.

The scanning beam field in the form of a curtain or a flat orthree-dimensional grating is advantageously light in the visible or alsoin the invisible spectral range. Ultrasonic or radar radiation can alsobe used. It goes without saying that detectors tuned to the scanningradiation emitted by a radiation source are also used.

Rather it is not the object which is directly measured, but an image ofthe object is scanned. The image of the object is fixed by the picturearea of an imaging system which can be scanned one- ortwo-dimensionally. For example the imaging system is a recording camera,an image of the object in a scanning tunnel microscope or from anelectron-power microscope. The image of the object can however also beproduced by inductive measurement, for example for ferromagneticmaterials, or by a capacitive measurement for nonconducting or poorlyconducting substances. Basically all images of an object which reproduceits actual appearance or the extent of a measurement quantity ofinterest can be used for measurement.

It is advantageous if the number of scanning beams for each dimension ofthe object to be measured is at least eight. The binary search system issuperior with respect to time demands starting roughly from the numberof eight scanning beams. For larger numbers of scanning beams the timedifference increases very quickly. While in a linear search theoperating time is proportional to the number of scanning beams, itincreases in a binary search only in relation to the logarithm of thenumber of scanning beams to the base 2.

By the object's being moved into the three-dimensionally limited actionarea of the scanning beam field such that at least in one of itsdimensions which are to be determined the object boundary coincides withthe edge boundary of the three-dimensionally limited action area of thescanning beam field, establishing the zero line for this dimension isabandoned. To determine the size of the object in this dimension thebinary search process can be immediately used. In the ideal case of acuboidal or cubic object it can even be placed at the origin of thethree-dimensional scanning beam field such that for all dimensiondeterminations the establishment of the zero line can be abandoned. Butgenerally there are more or less irregularly shaped objects which aremoved in an arbitrary orientation and position on the transport meansinto the scanning beam field. In doing so it means a greatsimplification for the measurement process if for example when an objectis being transported via a transport belt the scanning beam fieldcomponent is bordered by the transport belt surface over thehorizontally running transport belt surface which is generally used fordetermining the height of an object. The scanning beam with the index 1runs in the immediate vicinity and parallel to the transport beltsurface from one lengthwise side of the transport belt to the other. Theother scanning beams for determining the height of the object arearranged vertically over it and are numbered continuously increasing.

Measurement of the object can take place on the resting object. Forreasons of more rapid throughput, it is however advantageous if relativemotion takes place between the object which is to be measured and thescanning beam field during the measurement. This can be achieved forexample by the object's being continuously transported through theaction area of the scanning beam field. Transport of the action area ofthe scanning beam field over a resting object is also possible. Forexample, in automatic washing systems the vehicle is often stationaryand the measurement device which records the vertical and horizontalcontour of the vehicle is moved over the object. Then in the followingwashing step the vertical and horizontal brushes are controlled with thestored image. A similar application arises in automatic enamelling lineswhere the object to be enamelled is first measured at rest and then isenamelled in the enamelling chamber based on the stored image. Therelative speed is matched to the maximum detection time for measuringthe object. With conventional transport means the residence time of theobject which is to be measured in the measurement beam field is muchlarger than the detection time when the process as claimed in theinvention is being used.

Other advantages and features of the invention result from the followingdescription of one sample version of the process as claimed in theinvention. The schematics are used to illustrate the process.

FIG. 1 shows a horizontally arranged curtain of electromagnetic scanningradiation with an object located in it and a corresponding assignedsearch table;

FIG. 2 shows an object which is arranged arbitrarily in the scanningbeam field;

FIG. 3 shows an imaging system for measuring an object; and

FIG. 4 shows a diagram for explaining the time savings when the processas claimed in the invention is used.

FIG. 1 shows a horizontally running, curtain-like scanning beam fieldwhich is provided overall with reference number 1. The scanning beamfield 1 is fixed by individual scanning beams L which are each emittedby a transmitting element 2 and are detected by the opposite receiver 3.The scanning beam field can be an electromagnetic beam field, forexample a curtain of light or radar beams, or an ultrasonic beam field.The individual scanning beams can be directly addressed. The individualscanning beams L run at the same distance from one another. In theillustrated embodiment the scanning beam field comprises a total of 32individual scanning beams L. Instead of the receiver 3 there could alsobe reflecting elements which reflect the emitted scanning beams L backto the transmitter 2. In this case each transmitter is moreover alsomade as a receiver. Transmitters 2 and receivers 3 extend above atransport means 5 for an object 6 which is to be measured and whichrests with its bottom 7 on its surface 4. For example the transportmeans 5 is a transport belt or a pallet or the like. The scanning beamsL run roughly parallel to the surface 4 of the transport means 5. Thescanning beam field 1 extends essentially vertically over the transportmeans 5. The lowermost scanning beam L runs in the immediate vicinity tothe surface 4 of the transport means 5. The height of the object 6 canbe determined with a curtain-like scanning field 1 which is built up inthis way. This is necessary for example for automatic storage of theobject 6 in order to select a compartment of suitable height.

With the illustrated arrangement the height determination of the objectis reduced to ascertaining the number of interrupted scanning beams L.To do this, the scanning beams L beginning from the surface 4 of thetransport means 5 are consecutively numbered with increasing numbers.The scanning beam L which runs in the immediate vicinity of the surfaceof the transport means acquires for example the index n=1. Thesubsequent scanning beam L is labelled 2, etc. The uppermost scanningbeam L which borders the action area of the scanning beam field 1 to thetop bears the index n=32. It goes without saying that consecutivenumbering can also be undertaken in the reverse sequence.

To determine the height of the object 1, thus proceeding from the firstinterrupted scanning beam L with the index N=1, the uppermostinterrupted scanning beam L or the first scanning beam L which hasfreely passed to the receiver 6 must be determined. For the sequentialsearch process known from the prior art, the individual scanning beams Lare scanned sequentially in order to ascertain the interruptions. Thescanning consists in activating a transmitting element 2 and at the sametime evaluating an opposing receiving element 3 for the emitted scanningbeam L. The theoretical duration of a scan, the scanning time, is foundfrom the scanning time per scanning beam multiplied by the number n ofscanning beams plus the evaluation time. The equation for this reads:t _(Scan) =t _(Beam) ×n+t _(Evaluation)

It can happen that the object which is to be automatically measured thentravels exactly into the detection area of a scanning beam L after ithas been scanned. In order to preclude this error source and stillrecognize the object, the entire scanning beam field 1 must be scanned asecond time. Thus in practice the maximum detection time is twice thescanning time.

The equation for the detection time is:t _(detection) =t _(Scan)×2=(t _(Beam) ×n+t _(Evaluation))×2

In practice, the scanning time per light beam is roughly 100microseconds; the number n of beams of the light grating is for example32; the evaluation time is typically roughly 500 microseconds. Withthese typical practical values for t_(detection) the value is 7.4 ms.

To differentiate from the linear search process of the prior art, theinvention proposes a non-linear search process, especially a binarysorting process. It is based essentially on continuous halving of thesearch interval with simultaneous use of sorting of the scanning beams.First of all, the interval of a total of 32 scanning beams L is cut inhalf and the scanning beam with the index n=16 is activated andinterrogated. When this scanning beam L can travel freely to itsreceiver element 3, it is deduced that the object 6 extends only in thelower half of the scanning beam field 1 with the scanning beams with theindex 1 to 16. In the sorting table shown in FIG. 1 the freely passingscanning beam is marked as 16F. In the second step the lower half of thescanning beam field, the lower interval, is cut in half again and thescanning beam L with the index 8 is activated and interrogated. In doingso it is ascertained that the scanning beam with the index 8 isinterrupted. This is given in the sorting table by 8U. It is inferredfrom this result that the top end of the extension of the object 6 mustlie in the interval of the scanning beams with the index n=9 to n=16.This interval is cut in half and the scanning beam with the index n=12is interrogated. In doing so it is ascertained that this scanning beamcan pass freely. This is noted in the sorting table with 12F. In step 4therefore the interval between the scanning beam with the index 12 andthe scanning beam with the index 8 is cut in half and the scanning beamwith the index 10 is interrogated. In doing so it is ascertained that itis interrupted; this is noted in the sorting table with 10U. Thus, instep 5 the interval between the interrupted scanning beams with theindex n=10 and the next free scanning beam with the index n=12 remainsto be examined. This ultimately leads to a scanning beam with indexn=11. In doing so it is ascertained that it is likewise interrupted;this is entered in the sorting table with 11U. Thus, using the searchprocess as claimed in the invention, in only 5 steps it was possible toascertain that the end of the upper extension of the object 6 which isto be measured with respect to its height lies between the scanningbeams with the index n=11 and the index n=12. Thus, the height of theobject is determined up to an accuracy of approximately the distance ofthe two adjacent scanning beams L.

The detection time is fixed by the following equationt _(detection) =t _(Scan)×2=(t _(Beam) ×n+t _(Evaluation))×2With the value n=5 for the number of individual scans there is adetection time t_(detection)=2 ms for the described embodiment. Thiscorresponds to a time savings of 5.5 ms or 73% compared to the linearsearch process.

The process as claimed in the invention can be carried out most quicklywhen an object boundary coincides with the detection boundary of theelectromagnetic radiation field in the dimension which is to bedetermined. This criterion is generally satisfied for one-dimensionalheight determinations. But if the extension in another dimension or intwo or in all three dimensions is to be determined, the object isusually somewhere in the detection area of the electromagnetic field.This situation is shown for example in FIG. 2 in which it is in turn thedetermination of the height of the object. In this case, first of allusing the known linear search process, the lower or the upper start ofthe object is determined. If this is the limit of the extension, thescanning beam assigned to this position is defined as the zero line.Further dimension determination can then take place according to theabove described process as claimed in the invention. First of all, onlythe object within the scanning beam field can be sought. The upper andthe lower object boundary can then be determined up and down accordingto the process as claimed in the invention. In the case described usingthe example as shown in FIG. 2, the time savings compared to the purelinear process does not reach the maximum possible value. The time whichis necessary for combined linear and binary search is however alsoalways less than the use of the linear search process alone.

FIG. 3 shows an image 16 of the object, for example the picture of ascanning camera It could also be the image of an object as is producedin scanning tunnel microscopy or in an electron-power microscopy. Otherimages of an object can originate for example from inductivemeasurements for ferromagnetic substances or from capacitivemeasurements for nonconducting or poorly conducting substances. Incontrast to a scanning beam process, here the image 16 of the object canbe scanned or interrogated in two dimensions.

The quantities n_(y) and n_(x) indicate the line and column number ofthe picture. The lines and columns are built up from individual imageelements (pixels) and can be directly addressed. The object base 17coincides with the line detection boundary of the scanning beam field11. Therefore the search process as claimed in the invention in the linedirection (y-direction) can be carried out by analogy with the searchprocess explained using FIG. 1. With respect to the scanning columnsn_(x) the conditions are similar to those which were explained usingFIG. 2. To determine the dimension of the object in the column direction(x-direction) therefore first the image 16 of the object must be found.This takes place for example again via a linear search process. If theimage 16 of the object is found in the two-dimensional scanning beamfield 11, determination of the object boundaries can be done again usingthe process as claimed in the invention.

The process as claimed in the invention can be used in one-dimensionalscanning beam fields, such as light curtains for example, likewise intwo-dimensional or three-dimension scanning fields. A two-dimensionalscanning field can be fixed for example by a light grating or can beformed by an imaging system, for example a recording camera, a scanningtunnel microscope or an electron-power microscope. Images from inductiveor capacitive measurements and similar analyses can also be used formeasurement. The scanning radiation can be electromagnetic radiation,for example light in the visible and in the invisible spectrum, orradar, or ultrasonic radiation. The process as claimed in the inventioncan be used for any type of sensor which fixes a linear, flat orthree-dimensional scanning field. The object can be at rest during themeasurement. Due to the high speed of the process, the objects can alsobe moved through the scanning field.

FIG. 4 shows in diagram form the time savings when the process asclaimed in the invention is used compared to the linear search process.The data relate to a one-dimensional measurement in which an objectboundary coincides with the detection boundary of the scanning beamfield. The x axis plots the number of scanning beams; the y axis showsthe time savings in %. Here reference is made to a purely linear searchprocess for the same number of scanning beams. It is immediatelyapparent that the process as claimed in the invention entails enormousadvantages in speed so that even smaller objects which move relativelyquickly through the scanning beam field can be detected and measured.

1. Process for contactless measurement of an object in at least onedimension, comprising: scanning the object in a three-dimensionallylimited action area of a scanning beam field; and detecting one or moreinterruptions of scanning beams and deducing a size of the object in themeasured dimension, wherein the scanning beam field is built up using anumber of directly addressable individual beams, and wherein scanningtakes place according to a definable step pattern and a non-linearsorting process.
 2. Process as claimed in claim 1, wherein determinationof the size of the object takes place in at least one dimension byscanning the scanning beam field in regions according to a binary searchprinciple.
 3. Process as claimed in claim 2, wherein the size of theobject is determined in more than one dimension and thethree-dimensionally limited action area of the scanning beam field isscanned by a combination of principles of linear and binary search. 4.Process as claimed in claim 1, wherein the object is placed in theaction area of a beam curtain which is fixed by individual scanningbeams or of a two-dimensional or three-dimensional beam grating. 5.Process as claimed in claim 1, wherein the object is moved into ascanning beam field of electromagnetic radiation or of ultrasonicradiation.
 6. Process as claimed in claim 1, wherein the object is movedinto a scanning beam field of electromagnetic radiation in the visibleor invisible spectral range or radar radiation.
 7. Process as claimed inclaim 1, wherein an image of the object which is to be measured isscanned.
 8. Process as claimed in claim 7, wherein the image of theobject is fixed by a picture area of an imaging system which can bescanned one- or two-dimensionally, using at least one of a recordingcamera, an image of a scanning tunnel microscope or an electron-powermicroscope, or a capacitive or inductive measurement which isimplemented graphically.
 9. Process as claimed in claim 1, wherein thenumber of scanning beams for each dimension of the object to be measuredis at least eight.
 10. Process as claimed in claim 1, wherein the objectis moved into the three-dimensionally limited action area of thescanning beam field such that in at least one of its dimensions whichare to be determined an object boundary coincides with an edge boundaryof the three-dimensionally limited action area of the scanning beamfield.
 11. Process as claimed in claim 1, wherein during measurement,relative motion takes place between the object which is to be measuredand the scanning beam field.
 12. Process as claimed in claim 11, whereinthe object which is to be measured is transported during themeasurement, preferably continuously, through the action area of thescanning beam field.
 13. Process as claimed in claim 11, wherein theimage of the object is recorded, stored and evaluated for measurement,and in a following step determined measurement data are used for controlof handling and treatment processes for the object.
 14. Process asclaimed in claim 12, wherein the image of the object is recorded, storedand evaluated for measurement, and in a following step determinedmeasurement data are used for control of handling and treatmentprocesses for the object.